The purpose of oil well safety valves is to automatically stop the effluent production if an accident takes place at the well head or downstream therefrom. Such valves are hydraulically controlled to open from the surface and close automatically by means of a strong return spring the moment there is a drop, accidental or controlled, in the hydraulic pressure. These valves have long been studied and improved upon, and they are in wide use, in particular in offshore wells.
However currently used valves incur several drawbacks. In the first place, the return springs in most existing valves are subjected to deposits or corrosion effects from fluids with which they are in contact. In some valves, for instance those described in the French patent application No. 2,536,783 and in the French certificate of addition application No. 2,555,246, the return spring is located in the circuit of the control fluid. However the circuit geometry is such that it cannot be entirely drained and the spring is arranged in such a way that at least in part it is surrounded by gases. The corrosion from these gases causes rapid degradation and aging of the spring. This is a serious drawback in practice because spring degradation is translated into the danger that the valve will not close when necessary.
Furthermore, assembly and disassembly of the existing valves are complex and even dangerous procedures because of the presence of the springs with high return forces which must be relaxed to permit overhauling the equipment. Qualified personnel are required to carry out this maintenance which is delicate on account of the large number of parts and seals that are present, and such skilled labor is not always available on site. Again, these valves with many moving parts entail costly manufacture due to the machining and quality assurance time they demand. And the number of seals they require necessarily compounds the danger of malfunction.
Accordingly, the primary object of the present invention is to provide an improved safety valve free of the above stated drawbacks.
A further object of the invention is to provide a valve wherein the return spring and the moving parts are permanently and very effectively lubricated, thereby substantially reducing the possibility of corrosion.
Another object of the invention is to eliminate the element of danger from the valve being disassembled by eliminating the dangers relating to the relaxation of the return spring.
Still another object of the invention is to provide a simplified valve with a reduced number of parts.
Yet another object of the invention is to provide a valve with a reduced number of seals and permitting easy access and easy exchange of the most exposed seals.
Still another object of the invention is to facilitate the maintenance and overhaul of the valves.
Still a further object of the invention is to provide a simple installing tool for putting the return spring in place.
To facilitate understanding, the valve of the invention is assumed to be in place in an oil well, with the terms "high", "low", "upper", "lower" referring to that position.